As disclosed in U.S. Pat. Nos. 3,909,839 and 4,007,486, a frame synchronizer has a one-frame or one-field memory adapted to temporarily store an incoming video signal on a frame-by-frame or field-by-field basis, which is then read out in synchronism with a local reference synchronizing signal. The use of a frame synchronizer makes possible the so-called multi-station relay telecast, in which a plurality of incoming video signals, supplied from remote television stations mutually out of synchronism, can be selectively combined into one video signal synchronised with the local reference synchronizing signal. In addition the frame synchronizer has brought about a revolutionary change in television signal processing for special effects, due to its adaptability to digital signal control.
While complete synchronization of the incoming video signal with the local reference synchronizing signal is ensured by the frame synchronizer, the video signal itself can be delayed by a one-frame or one-field period. On the other hand, the audio signal component of the television signal does not suffer such delay because it is normally excluded from the signal processing for the video signal and allowed to separately pass to the output of the video signal processing stages. As a result, the video signal delay becomes conspicuous in the reproduced picture due to the delay between the picture displayed and the sound, and, between the motion of the announcer's lips and his articulation. Our experiments shown that the tolerable limit to the delay is approximately one frame period of a cinefilm, i.e., 1/24 of a second (41.7 milliseconds). Such a limit is easily exceeded when two frame synchronizers are connected in tandem for a multi-station relay telecast or for special video effects. This difficulty is also experienced in a standard conversion system which employs a one-frame memory.
It is therefore an object of the present invention to provide a delay compensator for video signal components for use with frame synchronizers or standard conversion systems including one-frame or one-field memory.